Time, Observations of

Time, as an object to be observed, is a human concept. In order for time to be observed, this concept needed to be converted to a measurable entity. These measurable, or observable, separations of time can be divided into various groupings.

Observations of time can first be categorized as either temporal or fixed. The temporal, or relative, observations of time constantly change in their lengths. Based, for example, on the apparent motions of the sun or moon, these temporal segments vary from day to day, and even from latitude to latitude in a single day. Whether it is local time, based on the hour of “high noon” when the sun is at the zenith, or the length of sunlight to be divided into equal components (traditionally 12), these would not recur at identical intervals from day to day or place to place (or both). While these observations were only relative, such as measured in the length and/or direction of a shadow on a sundial, they did provide reference points—useful in Jewish and Muslim societies, for example, in determining the daily prayer times in relation to the sun's position in the sky. Fixed observations, on the other hand, occurred regularly and at specific intervals—even if the intervals were not of equal size from day to day, they were equal in parts each day, such as the Catholic prayers being at specific hours of the day—whether they were temporal or fixed hours.

The cyclical nature of the universe was realized as a way to observe time was found useful by the nomadic societies who needed to know when to move their herds or the agrarian societies who needed to know when to plant seeds. It was noted the seasons changed regularly, and observable phenomena such as stars reappeared in the same spot in the sky on a regular basis—what we consider to be a solar year. This led to fixed separations of equal lengths of time that occur regularly, such as months and years.

Both temporal and fixed observations of time can be separated as well into two types of observations—naturally occurring and human made. Natural time is based on the regularly occurring events in nature, such as solar noon, or the reappearance of a star at a particular point in the sky, such as the Egyptians identified. Natural time observations can be based on the rotation of the earth on its axis—the 24-hour day, as we know it; or the revolution of the earth around the sun on its orbit—the solar year, as we know it. Even the recurrence of the full moon—the lunar month—is a naturally occurring event that indicates regular passage of time. These events occur naturally, and whether or not the passage of time between these events' recurrences is measured, they still recur regularly. It is only when humans decided to sort these times into observable components of equal lengths that the concept of a fixed-length passage of time, such as clock time (hour, minute, second, etc.), the 7-day week, or varying month lengths, for example, was instituted.

...